158  Intelligence  and  Miscellaneous  Articles. 
on  contraction,  are  measured  by  the  thermopile.  Yet,  as  the  thermal 
indications  are  mostly  restricted  to  deflections  of  8  or  10  degrees  of 
the  galvanometer,  it  will  be  easily  understood  that  the  small  differ- 
ences are  concealed  and  annulled  by  the  unavoidable  errors  in  such 
observations.  The  phenomenon  is  most  conclusively  demonstrated 
when  the  extensions  and  contractions  are  repeated  several  times  in* 
succession,  in  such  a  manner  that  the  greater  increase  of  tempera- 
ture on  extension  may  accumulate  as  against  the  smaller  decrease 
on  the  corresponding  contraction.  And,  in  fact,  when  I  frequently 
and  successively  stretched  and  loosened  two  caoutchouc  threads,  one 
6  to  7  millims.  and  the  other  10  millims.  in  thickness,  I  observed 
v/ith  the  thermopile  so  strong  an  increase  on  stretching,  that  the 
deflection  of  the  galvanometer  amounted  to  GO,  70,  or  even  90°, 
especially  in  the  experiments  with  the  thicker  thread. 
I  repeated  the  same  experiments  on  two  caoutchouc  bands — one  a 
perfectly  smooth  one,  25  millims.  in  breadth  and  3  millims.  in  thick- 
ness, and  one,  which  was  rough  from  the  impression  of  the  fabric 
on  which  it  had  been  made,  27  millims.  in  breadth  and  4  millims.  in 
thickness.  Both  these  strips  gave  the  same  results  as  the  above- 
mentioned  threads — that  is,  became  strongly  heated  on  frequent  and 
rapid  stretching  and  loosening.  These  strips  were  frequently  drawn 
out  with  the  hand,  but  usually  by  means  of  the  above-mentioned 
lever,  the  motion  of  which  was  confined  by  means  of  two  fixed 
points.  The  object  of  this  was  to  regulate  the  rapidity  of  the 
stretching  and  contraction,  and  thus  dissipate  a  doubt  I  had  enter- 
tained, that  the  generally  greater  velocity  on  contraction  might 
have  some  influence  on  the  result.  Hence  manifold  experiments 
were  made  with  the  bands  in  question.  Sometimes  the  stretch- 
ing was  made  more  rapidly  than  the  contraction ;  and  sometimes 
the  latter  was  quicker  than  the  former.  In  all  cases  a  powerful 
increase  in  temperature  was  observed  in  the  strips  under  investiga- 
tion. To  give  some  idea  of  the  heating,  I  may  observe  that  a  hun- 
dred rapid  stretchings  of  the  band  which  was  3  millims.  in  thick- 
ness heated  it  so  that  the  thermopile  placed  upon  it  deflected  the 
galvanometer  to  the  extent  of  90°.  This  deflection  rapidly  les- 
sened. Similar  stretchings  made  with  the  band  which  was  4 
millims.  in  thickness  heated  it  still  more — so  that  the  pile  de- 
flected the  galvanometer  with  a  powerful  swing  to  90°,  and  kept 
it  so  for  several  minutes;  even  after  10  or  12  minutes  it  still 
deviated  from  zero.  By  only  ten  stretchings  the  galvanometer  de- 
flected 20°.  It  is  clear  that  the  shorter  the  time  in  which  the 
experiment  is  made  the  greater  is  the  increase  of  temperature ;  for 
then  the  loss  caused  by  radiation  is  less.  In  repeating  the  experi- 
ment, it  is  essential  that  the  pile,  whether  it  hangs  freely  or  is  placed 
upon  the  caoutchouc,  show  no  deflection  on  the  galvanometer.  As 
that  part  of  the  galvanometer  which  touches  the  pile  cools  sooner 
than  the  free  part,  I  have  assured  myself,  by  placing  the  pile  on  dif- 
ferent parts  of  the  strip,  that  it  had  everywhere  the  same  temperature 
as  the  vicinity. 
The   explanation  of  this   is   found  in  the  consumption  of  force 
